Coating material for metal and metallic container coated with the coating material

ABSTRACT

The present invention provides a coating material for metal wherein a thin coating film without pinholes having excellent corrosion resistance, retort resistance, impact resistance, processing resistance, abrasion resistance, adhesiveness to a metal, flavor preservability for contents etc can be formed when applying on a metal plate or a metallic container, and a metallic container on which the coating material is applied. The present invention relates to a coating material for metal comprising thermoplastic resin particles having an average primary particle size of 10 to 1000 nm obtained by cooling a solution of the thermoplastic resin, and a process for preparing the coating material for metal comprising steps of (a) obtaining a solution wherein a thermoplastic resin is dissolved into an organic solvent, (b) obtaining a dispersion of particles of the thermoplastic resin having an average primary particle size of 10 to 1000 nm by cooling the solution, (c) separating particles from the dispersion and (d) dispersing the separated particles in a solvent.

TECHNICAL FIELD

The present invention relates to a coating material for metal and apreparation process thereof, and a metallic container on which thecoating material is applied and a preparation process thereof.Specifically, the present invention relates to a coating material formetal on which a thin coating film without pinholes, having excellentstrength, solvent resistance, impact resistance, processability etc canbe easily formed in a short time, when applying on a metal plate,compared with a laminate material, and a preparation process thereof.The present invention also relates to a metallic container on which thecoating material is applied and a preparation process thereof.

BACKGROUND ART

Conventionally, coating and printing are generally applied on a surfaceof a metallic container such as food can which preserves foods etc andbeverage can for imparting corrosion resistance and decoration.

For instance, JP-A-6-306325 discloses a resin composition for an aqueouscoating material comprising an acrylic emulsion, an acrylic modifiedepoxy resin and an amino resin. However, the acrylic emulsion contains amonomer contributing to crosslinking, and water with high surfacetension is used as a solvent. As the result of causing materialcontraction at heat treatment, pinholes occur in the coating film, thus,the acrylic emulsion is not fully satisfactory in terms of corrosionresistance and decoration.

Also, JP-A-2000-53892 describes a coating material containingpolyethylene terephthalate (PET) resin powder. The PET resin powder isprepared by separating out particles by water cooling from a solution ofmixed pellets containing a regenerated PET resin. However, a coolingspeed of the solution of the mixed pellets is slow since water coolingis used as a means of cooling in this process, and an average particlesize of the obtained particles is about 40 μm at minimum, which issignificantly large. Therefore, a coating film comprising this coatingmaterial becomes thick, depending on the average particle size of theparticles contained thereto, and the PET resin is not fully satisfactoryin viewpoints of appearance, processability and cost.

JP-A-11-156998 describes a metal plate on which a film without pinholesis laminated. However, there is a limitation to thin down the laminatefilm, and it is difficult to obtain a thinner film with a thickness ofabout a few μm. Consequently, the metal plate is not fully satisfactoryin viewpoints of appearance, processability and cost.

JP-A-2002-120278 describes a process for preparing a resin coated metalplate in which a film is prepared by heat-melting a thermoplastic resinand the obtained film is pressurized to adhere to a metal plate by apressure roll and then cooled rapidly to at most Tg. However, theequipment is too grand and there is a limitation for making a thin filmas well as JP-A-11-156998. Consequently, the resin coated metal plate isnot fully satisfactory in viewpoints of appearance, processability andcost.

DISCLOSURE OF INVENTION

Herein, the present invention provides a coating material for metal inwhich a thin coating film without pinholes having excellent strength,solvent resistance, impact resistance, processability etc can be easilyformed in a short time when applying on a metal plate and metalliccontainer, compared with a laminate material, and a preparation processthereof. The present invention further provides a metallic container towhich the coating material is applied and a preparation process thereof.

Namely, the present invention relates to a coating material for metalcomprising thermoplastic resin particles having an average primaryparticle size of 10 to 1000 nm obtained by cooling a solution of thethermoplastic resin, a metallic container to which the coating materialis applied.

Also, the present invention relates to a process for preparing thecoating material for metal comprising steps of (a) obtaining a solution,wherein a thermoplastic resin is dissolved into an organic solvent, (b)obtaining a dispersion of particles of the thermoplastic resin having anaverage primary particle size of 10 to 1000 nm by cooling the solution,(c) separating the particles from the dispersion and (d) dispersing theseparated particles into a solvent.

The present invention further relates to a process for preparing themetallic container comprising steps of (A) applying the coating materialfor metal of Claim 1 to a metal plate, and (B) melting the particles byheating the applied coating material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a SEM image (×35,000) of the primary particles of athermoplastic resin (polyethylene terephthalate) obtained in PreparationExample 1.

FIG. 2 is a diagram showing a distribution of the particle size of thethermoplastic resin (polyethylene terephthalate) particles obtained inPreparation Example 1.

FIG. 3 is a diagram showing a distribution of a particle size of thethermoplastic resin (MXD6 nylon) particles obtained in PreparationExample 2.

FIG. 4 is a diagram showing a distribution of a particle size of thethermoplastic resin (polylactic acid) particles obtained in PreparationExample 3.

FIG. 5 is a diagram showing a distribution of a particle size of thethermoplastic resin (polyglycolic acid) particles obtained inPreparation Example 4.

FIG. 6 is a diagram showing a distribution of a particle size of thethermoplastic resin (polybutylene terephthalate) particles obtained inPreparation Example 5.

FIG. 7 is a diagram showing a distribution of a particle size of thethermoplastic resin (6 nylon) particles obtained in Preparation Example6.

FIG. 8 is a diagram showing a distribution of a particle size of thethermoplastic resin (66 nylon) particles obtained in Preparation Example7.

FIG. 9 is a diagram showing a distribution of a particle size of thethermoplastic resin (polycarbonate) particles obtained in PreparationExample 8.

BEST MODE FOR CARRYING OUT THE INVENTION

The coating material for metal of the present invention comprisesthermoplastic resin particles having an average primary particle size of10 to 1000 nm obtained by cooling a solution of the thermoplastic resin.

Examples of an objective metallic material for applying the coatingmaterial for metal of the present invention are aluminum, steel, cupper,stainless steel, and a metal plate in which a surface treatment isapplied thereon. For instance, in case of steel, examples of the metalplate are a tin-plated steel plate (tin plate), a zinc-plated steelplate, and a steel plate electrolytically treated with chromic acid(tin-free steel), but the present invention is not limited thereto.

Examples of the thermoplastic resin are aromatic polyester resins suchas polyethylene terephthalate, polyethylene isophthalate, polybutyleneterephthalate and polyethylene naphthalate; aliphatic polyester resinssuch as polylactic acid, polyglycolic acid, polyethylene succinate,polybutylene succinate, poly(butylene succinate-carbonate),poly(butylene succinate-adipate), polyhydroxybutylate, andpoly(hydroxybutylate-valerate); polyamide resins such as 6 nylon, 66nylon, 12 nylon and MXD6 nylon; and a polycarbonate resin. Among those,polyethylene terephthalate, MXD6 nylon, polylactic acid, polyglycolicacid, polybutylene terephthalate, 6 nylon, 66 nylon and polycarbonateare preferable, if selected according to properties such as barrierability, transparency, other physical properties and safety. Inaddition, regenerated resins represented by a regenerated PET resin canbe used as a thermoplastic resin. However, the thermoplastic resin isnot limited thereto.

Examples of a solvent which dissolves a thermoplastic resin are estersolvents such as ethyl acetate and butyl acetate; dibasic acid estersolvents such as dimethyl adipate, dimethyl glutarate and dimethylsuccinate; ketone solvents such as cyclohexanone, isophorone and methylisobutyl ketone; hydrocarbon solvents such as cyclohexane, toluene andxylene; alcohol solvents such as benzyl alcohol and cyclohexanol; ethersolvents such as ethyleneglycol monobutyl ether, dipropyleneglycolbutylether and bis(2-methoxyethyl)ether; amide solvents such as formamide,dimethylformamide and dimethylacetoamide (DMAc); pyrrolidone solventssuch as N-methyl-2-pyrrolidone (NMP), sulfoxide solvents such asdimethyl sulfoxide, water, and a mixture thereof, but are not limitedthereto. Among those, a mixed ester solvent comprising dimethyl adipate,dimethyl glutarate and dimethyl succinate, dimethylacetoamide andbis(2-methoxyethyl)ether are preferable when a polyester resin is usedas a thermoplastic resin; formamde, benzyl alcohol, dimethylacetoamideand N-methyl-2-pyrrolidone are preferable when a polyamide resin is usedas a thermoplastic resin; and a mixed ester solvent comprising dimethyladipate, dimethyl glutarate and dimethyl succinate is preferable when apolycarbonate resin is used as a thermoplastic resin, in the viewpointthat it is possible to further use a solution after separating particlesfrom the obtained dispersion repeatedly as a solvent which dissolves athermoplastic resin.

A temperature of a solvent at dissolving the thermoplastic resin ispreferably 70 to 200° C. When the thermoplastic resin is polyethyleneterephthalate or polybutylene terephthalate, a temperature is preferably130 to 190° C., and more preferably 140 to 185° C. When thethermoplastic resin is polylactic acid, a temperature is preferably 70to 150° C., and more preferably 100 to 140° C. When the thermoplasticresin is polyglycolic acid, a temperature is preferably 130 to 170° C.,and more preferably 140 to 160° C. When the thermoplastic resin is MXD6nylon, a temperature is preferably 130 to 180° C., and more preferably140 to 170° C. Also, when the thermoplastic resin is 6 nylon, atemperature is preferably 120 to 180° C., and more preferably 130 to170° C. When the thermoplastic resin is 66 nylon, a temperature ispreferably 150 to 190° C., and more preferably 170 to 180° C. When thethermoplastic resin is 12 nylon, a temperature is preferably 120 to 150°C., and more preferably 130 to 140° C. When the thermoplastic resin ispolycarbonate, a temperature is preferably 130 to 180° C., and morepreferably 140 to 170° C. When a temperature of the solvent is less than70° C., desired particles having an average primary particle size of 10to 1000 nm do not tend to be obtained since the thermoplastic resin isnot dissolved, and when a temperature is more than 200° C., thethermoplastic resins or solvents tend to decompose and change color toyellow.

An amount of the thermoplastic resin into a solvent is preferably 1 to20 parts by weight based on 100 parts by weight of the solvent, and morepreferably 1 to 10 parts by weight. When an amount is less than 1 partsby weight, there is a problem in terms of productivity. Also, when anamount is more than 20 parts by weight, it tends to be difficult toobtain desired particles having an average primary particle size of 10to 1000 nm.

As a means for cooling a solution of the thermoplastic resin, a coolingsystem such as a heat exchanger is one example. It is preferable to coolthe thermoplastic resin solution of 70 to 200° C. to at most 50° C. andmore preferably to at most 45° C. by using the means for cooling. When atemperature of the solution after cooling is more than 50° C., a primaryparticle size of the obtained particles tends to be large.

As a cooling process, cooling a thermoplastic resin solution itself byusing a heat exchanger or by mixing the thermoplastic resin solutioninto a solvent cooled down to 20 to −90C. ° with a heat exchanger issuitable. The process of mixing with the cooled solvent is preferable ina viewpoint of cooling efficiency.

As a cooling speed, at least 20° C./s is preferable, at least 50° C./sis more preferable, and 100° C./s is further preferable. When a coolingspeed is less than 20° C./s, a primary particle size of the obtainedparticles tends to be more than 1000 nm.

An average primary particle size of the thermoplastic resin particlesobtained by cooling is 10 to 1000 nm, preferably 10 to 800 nm, morepreferably 10 to 500 nm, and further preferably 10 to 300 nm. When anaverage primary particle size is more than 1000 nm, such problems tendto occur that a thickness of the coating film becomes large or acontinuous film is not formed in case of making the coating film thin.When an average primary particle size is less than 10 nm, a viscosity ofthe obtained dispersion becomes high, and an operation for separatingtends to be difficult.

An average secondary particle size of the particles is preferably atmost 30 μm, and more preferably 1 to 10 μm. When the average secondaryparticle size is more than 30 μm, the thickness of the coating filmbecomes large and it shows the tendency that the desired coating filmcan not be obtained.

Herein, the primary particle is referred to as a particle in a statewhere the particle can not disperse any more. Also, the secondaryparticle is referred to as a particle in a state where the primaryparticle coagulates.

As a process for separating particles from a dispersion containing theparticles, examples are infiltration and centrifugation, but are notlimited thereto. As a filter for filtering, for example, a ceramicfilter is preferable.

Also, it is preferable to dry particles after separating the particles.Examples of a process for drying are vacuum drying, natural drying,drying with a dryer or an oven, but are not limited thereto. However, itis required to preset a temperature at which the particles do not meltwhen the particles are dried with a dryer or an oven.

The coating material for metal of the present invention comprisesthermoplastic resin particles having an average primary particle size of10 to 1000 nm. However, the coating material for metal may comprise amixture of at least 2 kinds of the thermoplastic resin particles, and anadditive such as a curing agent may be added to the thermoplastic resinparticles. It is preferable to add the thermoplastic resin particles toother coating materials since a stronger coating film can be formed.

The above described coating materials are not particularly limited aslong as they are generally employed as a coating material, and suchmaterial is a thermosetting coating material comprising a polyesterresin, an acrylic resin, an epoxy resin, an urethane resin, a melamineresin, a phenol resin, an urea resin etc.

Examples of a solvent in which the obtained particles are dispersed areester solvents such as ethyl acetate and butyl acetate, dibasic acidester solvents such as dimethyl adipate, dimethyl glutarate and dimethylsuccinate, ketone solvents such as cyclohexanone, isophorone and methylisobutyl ketone, hydrocarbon solvents such as cyclohexane, toluene andxylene, alcohol solvents such as benzyl alcohol and cyclohexanol, ethersolvents such as ethyleneglycol monobutyl ether, dipropyleneglycolbutylether and bis(2-methoxyethyl)ether, amide solvents such as formamide,dimethylformamide and dimethylacetoamide, pyrrolidone solvents such asN-methyl-2-pyrrolidone (NMP), water, and a mixture thereof, but are notlimited thereto, and any organic solvent suitable for the desiredcoating material can be used.

When the thermoplastic resin is polyethylene terephthalate, a mixedsolvent of cyclohexanone and xylene, a mixed ester solvent comprisingdimethyl adipate, dimethyl glutarate and dimethyl succinate, anddimethylacetoamide are preferable; when the thermoplastic resin ispolybutylene terephthalate, dimethylacetoamide and a mixed ester solventcomprising dimethyl adipate, dimethyl glutarate and dimethyl succinateare preferable; when the thermoplastic resin is MXD6 nylon,dimethylacetoamide and water are preferable; when the thermoplasticresin is 12 nylon, dimethylacetoamide and benzyl alcohol are preferable;when the thermoplastic resin is 66 nylon, benzyl alcohol is preferable;when the thermoplastic resin is 6 nylon, dimethylacetoamide, benzylalcohol and N-methyl-2-pyrrolidone are preferable; when thethermoplastic resin is polylactic acid, dimethylacetoamide, ethylacetate, butyl acetate, dimethyl succinate and methyl isobutyl ketoneare preferable; when the thermoplastic resin is polyglycolic acid,bis(2-methoxyethyl)ether and toluene are preferable; and when thethermoplastic resin is polycarbonate, dimethylacetoamide, cyclohexanoneand a mixed ester solvent comprising dimethyl adipate, dimethylglutarate and dimethyl succinate are preferable. A generally useddispersing agent may be used at the dispersing process. An amount of thedispersing agent in use is not particularly limited, and can be usedwithin the extent that the performance of the desired coating film isnot damaged.

In addition, for example, acid catalyzers such as sulfonic acidsincluding p-toluenesulfonic acid and dodecylbenzenesulfonic acid, andphosphoric acid including alkyl phosphoric acid, curing aids such as anamine blocking of the acid catalyzers, additives such as a levelingagent, a wetting agent, an antifoaming agent and lubricant, and coloringagents such as a pigment may be added, if necessary.

An amount of the thermoplastic resin particles is preferably at least 5%by weight, more preferably at least 10% by weight, further preferably atleast 15% by weight, and particularly preferably at least 20% by weightbased on total resins contained in a coating material. When an amount ofthe thermoplastic resin particles is less than 5% by weight, desiredeffects do not tend to be obtained.

A ratio of the thermoplastic resin particles and a solvent is notparticularly limited, and may be adjusted according to a desired coatingfilm.

Examples of a process for dispersing the thermoplastic resin particlesare dispersion with the supersonic wave and dispersion with an agitator.Examples are a homogenizer, a homo mixer, a roll mill, a beads mill anda high-pressure wet pulverizing equipment.

When the secondary particles are dispersed in a solvent, it ispreferable to finely divide by selecting a solvent and a process fordispersing, and more preferable to finally form primary particles.Dividing the particles finely enables a thickness of a coating film tocontrol a desirable thickness, and it is possible to finish a smoothercoating film.

Application of the coating material of the present invention can becarried out by generally known processes such as roll coating, spraycoating, brush coating, knife coating, dip coating, electrodepositionapplication, and electrostatics application.

When a coating film is formed by using the coating material of thepresent invention, a weight of the coating film after drying the coatingmaterial is preferably adjusted to be 0.1 to 50 g/m², and the weight ispreferably adjusted to be 1 to 50 g/m², more preferably 3 to 20 g/m²,further preferably 3 to 10 g/m².

A coating film from the coating material of the present invention isformed by evaporating a solvent by heating after the coating material isapplied, and then, melting particles. According to this process, anuniform coating film without pinholes is formed to obtain the coatingfilm excellent in solvent resistance.

A heating temperature is preferably 100 to 300° C., and more preferably150 to 280° C. A heating time is preferably 10 to 60 seconds, and morepreferably 15 to 30 seconds. Further, it is preferable to cool withwater after heating. This is because each physical property such asappearance of the coating film and processability is more excellent dueto cooling with water.

The metallic container of the present invention can be obtained byforming with a metal plate coated by the coating material of the presentinvention. The metallic container can be also obtained by applying thecoating material of the present invention to a metallic containerwithout any other coating. A process for preparing the metalliccontainer is not particularly limited, and its shape of the metalliccontainer is not limited as well. Examples of the metallic container arebeverage can, food can, decorated can, aerosol can, 18 L can, a drybattery shell, a battery shell or caps thereof.

The coating material of the present invention is an excellent coatingmaterial as a coating material for metal wherein a coating film withoutpinholes having excellent corrosion resistance, retort resistance,impact resistance, excellent processability, abrasion resistance,adhesiveness to metal, flavor preservability for contents etc can beformed when applying on a metal plate.

The coating material of the present invention is explained based onExamples in the following, but is not limited thereto.

<Average Primary Particle Size>

An average primary particle size is measured by using a scanningelectron microscope (JEM-6301F, made by JEOL Ltd.) and Dynamic LightScattering Nanoparticle Size Analyzer (LB-550, made by HORIBA, Ltd.).

<Film Thickness>

A film thickness is measured by using an Electromagnetic/Eddy-currentCoating Thickness Tester (LZ-200W, made by Kett Electric Laboratory).

<Pencil Hardness>

Pencil hardness is measured by UNI (product name) made by MITSUBISHIPENCIL CO., LTD., according to JIS K-5400 (1990).

<Solvent Resistance>

16 sheets of gauze are overlapped to fix on a convex part of a 2 poundshammer and shuttled on a coated plate after wetting well with methylethyl ketone, and the number of times when the coating film is peeledoff is regarded as solvent resistance.

<Impact Resistance>

Impact resistance is measured by using Du Pont type Impact Tester (madeby Toyo Seiki Seisaku-sho, Ltd.) according to a process described in JISK-5400 (1990). Then, Cellotape (registered trademark) made by NICHIBAN.,LTD. is put on a convex part and stuck tightly, then peeled off suddenlytoward a direction of 90 degree against a coated side. A state of thecoated side on the convex part is observed visually to evaluateaccording to the following evaluation standard.

A—Peeling is not observed at all.

B—Peeling is observed in part.

C—Peeling is observed on the whole.

<Bending Properties>

Bending properties are measured by using a Mandrel Bend Tester (made byToyo Seiki Seisaku-sho, Ltd). The measurement is carried out by 1T (atest wherein one plate for the bending test is sandwiched between thesame plates). Then, Cellotape (registered trademark) made by NICHIBAN.,LTD. is put on a convex part and stuck tightly, then peeled off suddenlytoward a direction of 90 degree against a coated side. A state of thecoated surface on the convex part is observed visually to evaluateaccording to the following evaluation standard.

A—Peeling is not observed at all.

B—Slight needled hair-like peeling having a length of less than 0.5 mmis observed, but practically is not a problem.

C—Peeling having a length of at least 5 mm is observed.

D—Peeling is already observed before Cellotape (registered trademark) isstuck.

<Punching Processability>

Press forming is carried out by using PP (pilfer proof) cap pressforming machine (made by Nihon Seiki Kogyo Co., Ltd.).

Two-staged press forming

-   -   (1) φ40 mm×21 mm    -   (2) φ30 mm×35 mm A state of the tested cap is evaluated        according to the following evaluation standard by visual        observation.        A—Peeling is not observed at all.        B—Slight roughness appears, but peeling is not observed.        C—Peeling of about 10 mm from the bottom is observed.        D—Peeling up to the upper part is observed.        <Pinhole Properties>

A coating plate of 100 cm² after baking the plate is immersed into a 1%saline water containing 0.3% of a surfactant, then a voltage of 6V isapplied to the plate and an amount of electric current after 4 secondsis represented by milliampere (mA). The smaller the mA value, the lesscoating defects are, which shows a preferable coating.

PREPARATION EXAMPLE 1 Preparation of Polyethylene Terephthalate ResinParticles

A 1 liter four-necked flask equipped with a thermometer and an agitatorwas charged with 30 g of polyethylene terephthalate (MA-1340P, availablefrom UNITIKA LTD.) copolymerized with 8% by mol of isophthalic acid as athermoplastic resin, and 570 g of a mixture of dimethyl adipate,dimethyl glutarate and dimethyl succinate (DBE (registered trademark),available from DuPont Kabushiki Kaisha) as a solvent. Then, atemperature of the solvent is adjusted at 180° C. and the thermoplasticresin was dissolved into the solvent. The obtained hot solution wasmixed with the cold DBE solvent which was cooled at −35° C. with a heatexchanger (made by MTECHNIC CO., LTD.). A dispersion (dispersedsolution) containing particles of the thermoplastic resin was obtained.A temperature of the dispersed soluiton after 1 second from a point ofmixing was 45° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge (made by TOMOE Engineering Co., Ltd.) to obtain a filtercake. The obtained cake had a solvent content rate of 75%.

An average primary particles size was at most 200 nm found by a SEMimage of the obtained particle (FIG. 1) and the distribution of theparticle size (FIG. 2).

PREPARATION EXAMPLE 2 Preparation of MXD6 Nylon(Methaxylylenediamineadipamide) Resin Particles

A 1 liter four-necked flask equipped with a thermometer and an agitatorwas charged with 30 g of MXD6 nylon (6007, available from MITSUBISHI GASCHEMICAL COMPANY, INC.) as a thermoplastic resin, and 570 g of formamideas a solvent. Then, a temperature of the solvent was adjusted at 140° C.and the thermoplastic resin was dissolved into the solvent. The obtainedhot solution was mixed with the cold dimethylformamide solvent which wascooled at −35° C. with a heat exchanger. A dispersed solution containingparticles of the thermoplastic resin was obtained. A temperature of thedispersed solution after 1 second from a point of mixing was 35° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake. The obtained cake had a solventcontent rate of 80%.

An average primary particle size of the obtained particles was at most400 nm found by the distribution of the particle size (FIG. 3).

PREPARATION EXAMPLE 3 Preparation of Polylactic Acid Resin Particles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by usingpolylactic acid as a thermoplastic resin and DBE as a solvent, in whicha temperature at dissolving was 140° C. and a cooling temperature was−35° C. A temperature of the dispersed solution after 1 second from apoint of mixing was 35° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake has a solvent content rate of 71%.

An average primary particle size of the obtained particles was at most250 nm found by the distribution of the particle size (FIG. 4).

PREPARATION EXAMPLE 4 Preparation of Polyglycolic Acid Resin Particles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by using apolyglycolic acid (PGA-P, available from Mitsui Chemicals, Inc.) as athermoplastic resin and a bis(2-methoxyethyl)ether as a solvent, inwhich a temperature at dissolving was 150° C. and a cooling temperaturewas −35° C. A temperature of the dispersed solution after 1 second froma point of mixing was 37° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake had a solvent content rate of 73%.

An average primary particle size of the obtained particles was at most150 nm found by the distribution of the particle size (FIG. 5).

PREPARATION EXAMPLE 5 Preparation of Polybutylene Terephthalate ResinParticles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by usingpolybutylene terephthalate (NOVADURAN5008, available from MitsubishiEngineering-Plastics Corporation) as a thermoplastic resin and DBE(registered trademark) (available from DuPont Kabushiki Kaisha) as asolvent, in which a temperature at dissolving was 185° C. and a coolingtemperature was −35° C. A temperature of the dispersed solution after 1second from a point of mixing was 45° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake had a solvent content rate of 80%.

An average primary particle size of the obtained particles was at most200 nm found by the distribution of the particle size (FIG. 6).

PREPARATION EXAMPLE 6 Preparation of 6 Nylon Resin Particles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by using 6 nylon(NOVAMID1010J, available from Mitsubishi Engineering-PlasticsCorporation) as a thermoplastic resin and N-methyl-2-pyrrolidone(available from Mitsubishi Chemical Corporation) as a solvent, in whicha temperature at dissolving was 170° C. and a cooling temperature was−20° C. A temperature of the dispersed solution after 1 second from apoint of mixing was 38° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake had a solvent content rate of 79%.

An average primary particle size of the obtained particles was at most350 nm found by the distribution of the particle size (FIG. 7).

PREPARATION EXAMPLE 7 Preparation of 66 Nylon Resin Particles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by using 66 nylon(NOVAMID3010, available from Mitsubishi Engineering-PlasticsCorporation) as a thermoplastic resin and benzyl alcohol (available fromTohoku Tosoh Chemical Corporation) as a solvent, in which a temperatureat dissolving was 170° C. and a cooling temperature was −15° C. Atemperature of the dispersed solution after 1 second from a point ofmixing was 37° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake had a solvent content rate of 77%.

An average primary particle size of the obtained particle was at most200 nm found by the distribution of the particle size (FIG. 8).

PREPARATION EXAMPLE 8 Preparation of Polycarbonate Resin Particles

A dispersed solution comprising particles of a thermoplastic resin wasobtained in the same manner as Preparation Example 1, by usingpolycarbonate (LUPILON S-2000R, available from MITSUBISHI GAS CHEMICALCAMPANY, INC.) as a thermoplastic resin and DBE as a solvent, in which atemperature at dissolving was 170° C. and a cooling temperature was −20°C. A temperature of the dispersed solution after 1 second from a pointof mixing was 38° C.

Particles were separated from the obtained dispersion by using SharplesCentrifuge to obtain a filter cake in the same manner as PreparationExample 1. The obtained cake had a solvent content rate of 64%.

An average primary particle size of the obtained particles was at most300 nm found by the distribution of the particle size (FIG. 9).

EXAMPLE 1 Addition of Thermoplastic Resin Particles to a PolyesterThermosetting Coating Material

A 2 L container was charged with 100 g of the cake of the thermoplasticresin obtained in Preparation Example 1, 1223.3 g of a polyester resin(VYLON GK880, cyclohexanone/xylene solvent having the ratio of 1:1,solid content of 30% by weight, available from TOYOBO., LTD.), 28.0 g ofa melamine resin (Cymel 303, solid content of 100% by weight, availablefrom Mitsui Cytec Inc.), 5.4 g of a carnauba wax dispersion (SL506, adispersed article in dipropyleneglycolmono-n-butylether, solid contentof 18.5% by weight, available from SAN NOPCO LIMITED), 0.5 g ofdodecylbenzenesulfonic acid, 88.8 g of a solvent mixture ofcyclohexanone/xylene, in which the ratio is 1:1, and 200 g of 2 mmφglass beads, and screw the container cap on tightly, then, a coatingmaterial for metal was obtained by dispersing for 2 hours with PaintShaker (made by ASADA IRON WORKS. CO., LTD.) and separating from theglass beads by filtering with a gauze. The obtained coating material hada solid content of 23.5% and viscosity of 25 seconds (Ford Cup No. 4).

The obtained coating material was painted on an aluminum plate (5052material, a plate thickness of 0.23 mm, a size of 12 cm×20 cm) withoutcoating by using Bar Coater #14 to have a film thickness of 4 μm afterdrying (coating amount after drying of 4.8 g/m²), and cooled with waterafter leaving the plate in a hot air circulation oven (made byKabushikikaisya SHOEI Seisakusyo), in which a temperature was preset at260° C. and a wind speed at 20 m/sec, for 20 seconds.

Results of performance testings of the obtained coating film are shownin Table 2.

EXAMPLE 2

A 900 mL bottle of mayonnaise was charged with 100 g of the cake of thethermoplastic resin obtained in Preparation Example 1, 0.25 g of acarnauba wax dispersion (SL506, a dispersed article indipropyleneglycolmono-n-butylether, solid content of 18.5% by weight,available from SAN NOPCO LIMITED), 150 g of DBE, and 150 g of 2 mmφglass beads, and screw the bottle cap on tightly, then, a coatingmaterial for metal was obtained by dispersing for 2 hours with PaintShaker (made by ASADA IRON WORKS. CO., LTD.) and separating from theglass beads by filtering with a gauze. The obtained coating material hada solid content of 10.0% and viscosity of 33 seconds (Ford Cup No. 4).

The obtained coating material was painted on an aluminum plate (5052material, a plate thickness of 0.23 mm, a size of 12 cm×20 cm) withoutcoating by using Bar Coater #14 to have a film thickness of 4 μm afterdrying (coating amount after drying of 5.6 g/m²), and cooled with waterafter leaving the plate in a hot air circulation oven (made byKabushikikaisya SHOEI Seisakusyo), in which a temperature was preset at260° C. and a wind speed at 20 m/sec, for 20 seconds.

Results of performance testings of the obtained coating film are shownin Table 2.

EXAMPLES 3 TO 9

The cake of the thermoplastic resin obtained in Preparation Examples 2to 8 was weighted out to have a resin solid content of 25 g, then eachdispersing solvent shown in Table 1 was added to have the total weightof 250 g, and a coating material for metal having a solid content of 10%by weight was obtained by employing 0.25 g of a carnauba wax dispersionand 150 g of 2 mmφ glass beads in the same manner as Example 1.

A test plate was prepared by painting the obtained coating material inthe same manner as Example 1 to make a film at each temperature. TABLE 1Viscosity Amount of Dispers- of coating application Oven presetThermoplastic ing material after drying temperature resin solvent(second) (g/m²) (° C.) Ex. 1 Polyethylene DBE 25 4.8 260 terephthalateEx. 2 Polyethylene DBE 33 5.6 260 terephthalate Ex. 3 MXD6 nylon Water90 4.8 260 Ex. 4 Polylactic Ethyl 17 5.2 200 acid acetate Ex. 5Polyglycolic Toluene 10 6.4 230 acid Ex. 6 Polybutylene DBE 28 5.6 260terephthalate Ex. 7 6 nylon NMP 26 4.4 250 Ex. 8 66 nylon Benzyl 30 4.4280 alcohol Ex. 9 Polycarbonate DBE 14 4.8 250 Com. Vylon GK880 Cyclo-35 4.8 — Ex. 1 hexa- none/ Xylene

COMPARATIVE EXAMPLE 1

A 2 L stainless beaker was charged with 1306.7 g of a polyester resin(VYLON GK880, cyclohexanone/xylene solvent having the ratio of 1:1,solid content of 30% by weight, available from TOYOBO., LTD.), 28.0 g ofmelamine resin (Cymel 303, solid content of 100% by weight, availablefrom Mitsui Cytec Inc.), 5.4 g of a carnauba wax dispersion (SL506, adispersed article in dipropyleneglycolmono-n-butylether, solid contentof 18.5% by weight, available from SAN NOPCO LIMITED), 0.5 g ofdodecylbenzenesulfonic acid, 105.4 g of a solvent mixture in whichcyclohexanone/xylene is 1:1, then a coating material for metal whichdoes not contain particles of the thermoplastic resin was obtained byagitating with Disper (made by ASADA IRON WORKS. CO., LTD.) for 10minutes. The obtained coating material had a solid content of 23.5% andviscosity of 35 seconds (Ford Cup No. 4).

A test plate was prepared using the obtained coating material in thesame manner as Example 1.

Results of performance testings of the obtained coating film are shownin Table 2. TABLE 2 Performance evaluation Solvent Pencil resistanceImpact Punching Pinhole hard- (No. of resis- Bending process- propertiesness times) tance properties ability (mA) Ex. 1 4H 36 A A B 0.01 Ex. 23H 100 A A A 0.01 Ex. 3 5H >100 A A A 0.01 Ex. 4 5H 3 A A A 0.01 Ex. 5 H5 A A A 0.01 Ex. 6 3H >100 A A A 0.01 Ex. 7 H >100 A A A 0.01 Ex. 8H >100 A A A 0.01 Ex. 9 5H 3 B B B 0.01 Com. 2H 21 B C C 0.03 Ex. 1

INDUSTRIAL APPLICABILITY

The coating material of the present invention can be favorably used as acoating material for metal since the coating material can form a coatingfilm without pinholes having excellent corrosion resistance, retortresistance, impact resistance, processing resistance, abrasionresistance, adhesiveness to a metal, flavor perservability for contentsetc by applying on a metal plate or a metallic container.

1. A coating material for metal comprising thermoplastic resin particleshaving an average primary particle size of 10 to 1000 nm obtained bycooling a solution of said thermoplastic resin.
 2. A process forpreparing a coating material for metal comprising steps of: (a)obtaining a solution wherein a thermoplastic resin is dissolved into anorganic solvent; (b) obtaining a dispersion of particles of saidthermoplastic resin having an average primary particle size of 10 to1000 nm by cooling said solution; (c) separating the particles from saiddispersion and (d) dispersing said separated particles into a solvent.3. A metallic container, to which the coating material for metal ofclaim 1 is applied.
 4. A process for preparing the metallic containercomprising steps of: (A) applying the coating material for metal ofclaim 1 to a metal plate; and (B) melting the particles by heating saidapplied coating material.